Explain what a homeostatic mechanism  is and how it is used to maintain conditions for life within the body, in language that a middle school student can understand.  Specifically address how homeostatic feedback loops are activated in response to changes in two of the major requirements for life of all organisms (water, heat, food, etc).  Ensure that you discuss the difference between a negative and a positive feedback loop and give brief examples of each.  Give a possible explanation for why negative feedback mechanisms are used more within physiological systems than positive feedback loops.  Your presentation should be well organized, and last no longer than five minutes.